Integrated circuits are made up of millions of active devices formed in or on a substrate, such as a silicon wafer. The active devices are chemically and physically connected into a substrate and are interconnected through the use of multilevel interconnects to form functional circuits. Typical multilevel interconnects comprise a first metal layer, an interlevel dielectric layer, and a second and sometimes subsequent metal layer(s).
As layers of materials are sequentially deposited onto and removed from the substrate, some portions of the uppermost surface of the substrate may need to be removed. Planarizing a surface, or “polishing” a surface, is a process where material is removed from the surface of the substrate to form a generally even, planar surface. Planarization is useful in removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches, and contaminated layers or materials. Planarization also is useful in forming features on a substrate by removing excess deposited material used to fill the features and to provide a level surface for subsequent levels of metallization and processing.
Chemical-mechanical planarization, or chemical-mechanical polishing (CMP), is a common technique used to planarize substrates. CMP utilizes a chemical composition, typically a slurry or other fluid medium, for removal of material from the substrate. In conventional CMP techniques, a substrate carrier or polishing head is mounted on a carrier assembly and positioned in contact with a polishing pad in a CMP apparatus. The carrier assembly provides a controllable pressure to the substrate, urging the substrate against the polishing pad. The pad is moved relative to the substrate by an external driving force. The relative movement of the pad and substrate serves to abrade the surface of the substrate to remove a portion of the material from the substrate surface, thereby polishing the substrate. The polishing of the substrate by the relative movement of the pad and the substrate typically is further aided by the chemical activity of the polishing composition and/or the mechanical activity of an abrasive suspended in the polishing composition.
The polishing composition may exhibit either a high or a low selectivity with respect to the particular layer or material being removed by the polishing process. When CMP is performed with a polishing composition having a high selectivity, the removal rate of the selected material is significantly higher than that of other material(s) exposed at the surface of the substrate being polished. Conversely, when CMP is performed with a polishing composition having a low selectivity, each material present on the substrate surface being polished is removed at substantially the same rate. Non-selective slurries may advantageously improve topography, i.e., reduce dishing and erosion, as compared to selective slurries over a wider range of surface features or patterns.
In addition to the polishing composition, the CMP apparatus and the surface pattern on the substrate affect selectivity during the polishing step. However, the aforementioned factors are unique to the end user, i.e., the device manufacturer. Accordingly, a fixed-selectivity polishing composition will not exhibit the identical selectivity in the hands of one device manufacturer as compared to another. For example, a polishing composition designed to be non-selective for a substrate containing a metal layer and a dielectric layer may not exhibit 1:1 selectivity during polishing of actual substrates, leading to undesirable erosion. Thus, a need exists for polishing compositions with tunable selectivities, allowing the end-user to easily optimize polishing performance for specific substrates and/or apparatus. Particularly, a need exists for polishing compositions capable of being tuned by the end-user to non-selectively remove a metal layer and a dielectric layer with nearly equal polishing rates during a single CMP polishing step.
The invention provides such a method of preparing a tunable polishing composition. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.